Roger Arthur Cowley, FRS, FRSE, FInstPhys (24 February 1939 – 27 January 2015) was an English physicist who specialised in the excitations of solids. He obtained a B.A. in physics from Trinity Hall, University of Cambridge in 1960 and a Ph.D. in 1963. He was appointed professor of physics at the University of Edinburgh in 1970 and Dr Lee's Professor of Experimental Philosophy at the University of Oxford in 1988 (a post that carried with it a fellowship at Wadham College, Oxford.
Cowley made his name in the field of neutron scattering. This work lead to the study of phase transitions.
He was elected Fellow of the Royal Society in 1978. He was awarded the inaugural Max Born Prize in 1973.